This study will be a Phase I, dose-escalation trial to evaluate the safety of autologous Mesenchymal Stromal Cell (MSC) transfusion in patients with acute ischemic stroke. Stroke remains the leading cause of adult disability in the U.S. Most patients do not access healthcare early enough to benefit from hyperacute stroke therapies. In animal models of stroke, administration of MSC days after infarct has been associated with improved behavioral outcome. MSC has been found to be safe in several safety studies of humans with non-cerebrovascular diagnoses. MSC may, therefore, represent a treatment that can improve outcome in human stroke patients with a wide time-window for intervention. The specific aims will evaluate whether the morbidity and mortality rates among patients receiving this treatment are higher than expected, according to specific primary and secondary endpoints. The primary endpoint focuses on mortality and major thrombotic/infectious adverse events 90 days after treatment. The secondary endpoints consider these events over a longer term, and further evaluate potential adverse effects on systemic and neurological function. The long-term objective is to identify a treatment that is safe, improves long-term outcome in patients with acute ischemic stroke, and can be administered to a majority of patients with a new diagnosis of stroke. This study is a Phase I safety trial, and thus represents the first step in evaluating autologous MSC transfusion in this regard.